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The Ionospheric Dynamics Exploration and Attitude Subsystem Satellite (IDEASSat/ INSPIRESat-2) is a three-unit (U) CubeSat developed with the objective of providing in-situ measurements of the Earth’s ionosphere in order to quantify both global scale ionospheric variability and small scale irregularities. The science payload is the Compact Ionospheric Probe (CIP) - an all in one in-situ plasma sensor developed at Taiwan National Central University (NCU), which is the miniaturized version of the larger Advanced Ionospheric Probe (AIP) that is carried and operational aboard the 450 kg FORMOSAT-5 spacecraft. The spacecraft has been developed by NCU in partnership with the International Satellite Program in Research and Education (INSPIRE) consortium, and is funded by the Taiwan National Space Organization (NSPO), Ministry of Science and Technology, and Ministry of Education as part of the first national effort to encourage small satellite development at Taiwan universities. The development of IDEASSat offers students a hands-on opportunity to learn about space science and technology and will work in conjunction with FORMOSAT-5 and INSPIRESat-1 to provide ionospheric observations spanning different altitudes and local times. The IDEASSat spacecraft subsystems are a combination of commercial off the shelf (COTS) and self-developed components designed by NCU in partnership with other INSPIRE member universities. IDEASSat is expected to be launched in late 2020. In this report, we describe the IDEASSat mission and spacecraft design, as well as unique lessons learned as part of the development process.

The JAXA’s Martian Moons Exploration (MMX) mission is planned to reveal the origin of Phobos and Deimos. It will remotely observe both moons and return a sample from Phobos. The nominal instruments include the TElescopic Nadir imager for GeOmOrphology (TENGOO) and Optical RadiOmeter composed of CHromatic Imagers (OROCHI). The scientific objective of TENGOO is to obtain the geomorphological features of Phobos and Deimos. The spatial resolution of TENGOO is 0.3 m at an altitude of 25 km in the quasi-satellite orbit. The scientific objective of OROCHI is to obtain material distribution using spectral mapping. OROCHI possesses seven wide-angle bandpass imagers without a filter wheel and one monochromatic imager dedicated to the observation during the landing phase. Using these two instruments, we plan to select landing sites and obtain information that supports the analysis of return samples. Graphical Abstract

Multi-band observation of transient luminous events (TLEs) is one of the useful methodologies to be employed in sprite campaigns. Here, we show a method to estimate the Boltzmann vibrational temperature of N2 (B3Πg) by analyzing the 630nm-filtered, N2 1P-filtered and 762 nm-filtered images of TLEs. Our advanced method is validated in compassion with derived relative vibrational distributions by sprite spectrum (Kanmae et al., 2007). The imager recorded N2 1P-filtered emission (I1P, 623 – 754 nm) of TLEs indicates the intensity of N2 1P Δv=3 and partial with Δv=2 where dominated emissions with upper state vibrational number v=4, 5 and 6, i.e., N2 1P (4, 2), (4, 1), (5, 2) and (6, 3). The imager recorded 630 nm-filtered emissions (I630) were contributed primarily from N2 1P (10, 7) with v=10 while N2 1P (3, 1) for 762 nm-filtered emissions (I762) with v=3. Hence, we calculated the emission ratios of I630 to I1P, I630 to I762 and I762 to I1P. The emission ratios of I630 to I1P, I630 to I762 and I762 to I1P also reflect the relative vibrational distributions of vibrational levels with LOW v=3 (I762), MIDDLE v=4, 5, 6 (I1P, 623 – 754 nm), and HIGH v=10 (I630). Therefore, we use the Boltzmann temperature for indicating the relative vibrational distributions of the specified group (LOW/MIDDLE/HIGH) of N2 (B3Πg) vibrational levels. For ISUAL recorded sprites, the average brightness of N2 1P (I1p), 762 nm (I762) and 630 nm (I630) emission was 2.3, 0.6 and 0.02 MR. The N2 (B3Πg) vibrational temperatures (Tv) were estimated to be 2800 K, 3200 K and 4300 K for multi-band emission ratios of I630/ I1p, I630/ I762 and I762/ I1p. For observed elves, the average brightness I1p, I762 and I630 were 170, 50 and 3 kR. The estimated Tv values were 3700 K, 3700 K and 3800 K for ratios I630/ I1p, I630/ I762 and I762/ I1p. For observed gigantic jets, the derived Tv values were 3000 – 5000 K for a ratio I762/ I1p. Through N2 (B3Πg) Tv analyses from emission ratios of ISUAL multi-band observation, we derived the N2 (B3Πg) vibrational temperature that ranges between 3000 and 5000 K or higher in TLEs. Accuracy and variations of derived N2 (B3Πg) Tv are also discussed while the relative population of vibrational levels in the Boltzmann equilibrium are also compared with past spectra observation. The details are shown in the publication (https://doi.org/10.1029/2019JA027311).

After almost thirty years’ efforts on studying transient luminous events (TLEs), ground-based observation has confirmed the TLE family, including elves, halos, sprites, and blue jets, etc. The typical elve has the shortest emission time (&lt, 1 ms) in comparison with other TLEs. The second shortest is the halo emission. Although elves and halos are supposed to be more frequent than sprites, ground campaigns still have less probability of recording their images due to their fleeting and short emission. Additionally, the submillisecond imaging of elves, halos, and sprite halos helps us resolve their electro-optic dynamics and morphological features, but few have been reported in the literature. Our study presents the 10,000 fps imaging frames on elves, halos and sprite halos, compares their similarity and disparity, and analyzes their parent lightning properties with associated VLF and ELF data.

Atomic sodium (Na) is one of the major meteoric species existing as layers of atoms in the mesosphere/lower thermosphere (MLT) at altitudes of 80–105 km and atomic ions at higher altitudes. As the boundary between neutral atmosphere and ionosphere, the MLT region is of particular interest because it is influenced by the mesoscale convective weather and thunderstorms from below and exposed to solar photons from above. There has been great interest on the atmosphere-ionosphere coupling, and numerous studies have been reported on the connection between thunderstorms and the ionosphere. However, the influence of thunderstorms on metallic species, which would significantly enhance our understanding of how Earth's atmosphere interacts with its ionosphere and studying the chemistry and physics of the MLT region, has rarely been studied. Here we present observational results on a statistical basis showing evidence that thunderstorm activities can affect the metal layer, by identifying a statistically significant enhancement of the neutral metal Na layer above thunderstorms at Haikou, China (20.0°N, 110.3°E). The thunderstorm-generated gravity waves and electric field effects could be the mechanisms responsible for the lightning-associated enhancement of Na layer.

The elve is the dominant type of transient luminous event (TLE) at the base of the E region ionosphere. The hydroxyl nightglow (OH* nightglow hereafter) has been reported at a similar altitude. Statistical studies show that the mean heights of elve and OH* nightglow are 87 km and 87.5 km, respectively, and that 91% of the 291 limb elves are located within ±5 km of the altitude of the brightest OH* nightglow emission and both elves and OH* nightglow show the semiannual oscillation (SAO) at low latitude. The physical reasons for the collocation of elves and OH* nightglow are the main focus of attention. A model for elve emission with the environmental-adapted electron density profile is tested with three density profiles of atomic oxygen (O): the original profile from the NRLMSISE-00 model and two other profiles which are shifted 5 km upward/downward from the original. For higher altitudes of the given O density profile, the peak altitudes of the elve emission layers are also increased. This result reveals the leading role of atomic oxygen in the collocation. Furthermore, the altitude variation of elves is compared with the VLF reflection height observed by DEMETER. The latter height not only shows the SAO similarity to the elve/OH* heights but also exhibits a difference between land and ocean. The possible relationship between VLF reflection height and elve/OH* height is also discussed.

The currents flowing between the Earth and ionosphere are numerically calculated. We solve the current continuity equation by two methods: the first method is to solve ϕ in ∇ ⋅ J = ∇ ⋅ (σ∇ϕ) = 0[Kuo et al., 2011] where σ is atmospheric conductivity and ϕ is the electric potential, and the second method is to solve the current potential Ψ in ∇ ⋅ J = − ∇2Ψ = 0by assuming J = − ∇Ψ, a curl-free current density [Kuo et al., 2014]. Two solutions of ∇ ⋅ J = 0for current flow in the atmosphere between Earth surface and ionosphere are compared in this reply. The differences of two results are

campaigns in Taiwan. We first introduce two types of spectroimagers, the slit and slitless types, and discuss their advantages and shortcomings. Next we explore the instrument development and procedures undertaken for this study. In 2006, a slit spectroimager was installed for a sprite campaign and on 15 August of that year, two sprite spectra were recorded using the slit spectroimager along with seven sprites, one halo, one ELVES emission and two jets. By the end of 2015, a slitless spectroimager had been successfully constructed and was ready to conduct additional investigations. On 7 May 2016, a sprite spectrum was recorded using the slitless spectroimager. Following an examination of the calibrations (comprising detection region field of view, wavelength calibration, and response curve), data analysis, and additional calibrations (comprising elevation and azimuthal angles, atmospheric transmittance, and theoretical wavelength calculations) performed in this study, we present the results from our observed sprite spectra using the slit and slitless spectroimagers.

We present a multi-instrument experiment to study the effects of tropospheric thunderstorms on the mesopause region and the lower ionosphere. Sodium (Na) lidar and ionospheric observations by two digital ionospheric sounders are used to study the variation in the neutral metal atoms and metallic ions above thunderstorms. An enhanced ionospheric sporadic E layer with a downward tidal phase is observed followed by a subsequent intensification of neutral Na number density with an increase of 600 cm−3 in the mesosphere. In addition, the Na neutral chemistry and ion-molecule chemistry are considered in a Na chemistry model to simulate the dynamical and chemical coupling processes in the mesosphere and ionosphere above thunderstorms. The enhanced Na layer in the simulation obtained by using the ionospheric observation as input is in agreement with the Na lidar observation. We find that the intensification of metallic layered phenomena above thunderstorms is associated with the atmospheric tides, as a result of the troposphere-mesosphere-ionosphere coupling.

Introduction Cell-free deoxyribonucleic acid DNA (cf-DNA) in urine is promising due to the advantage of urine as an easily obtained and non-invasive sample source over tissue and blood. In clinical practice, it is important to identify non-invasive biomarkers of chronic kidney disease (CKD) in monitoring and surveillance of disease progression. Information is limited, however, regarding the relationship between urine and plasma cf-DNA and the renal outcome in CKD patients. Methods One hundred and thirty-one CKD patients were enrolled between January 2016 and September 2018. Baseline urine and plasma cell-free mitochondrial DNA (cf-mtDNA) and cell-free nuclear DNA (cf-nDNA) were isolated using quantitative real-time PCR. Estimated glomerular filtration rate (eGFR) measurement was performed at baseline and 6-month follow-up. Favorable renal outcome was defined as eGFR at 6 months minus baseline eGFR> = 0. Receiver operator characteristics (ROC) curve analysis was performed to assess different samples of cf-DNA to predict favorable renal outcomes at 6 months. A multivariate linear regression model was used to evaluate independent associations between possible predictors and different samples of cf-DNA. Results Patients with an advanced stage of CKD has significantly low plasma cf-nDNA and high plasma neutrophil gelatinase-associated lipocalin (NGAL) levels. Low urine cf-mtDNA, cf-nDNA levels and low plasma NGAL were significantly correlated with favorable renal outcomes at 6 months. The urine albumin-creatinine ratio (ACR) or urine protein-creatinine ratio (PCR) level is a robust predictor of cf-mtDNA and cf-nDNA in CKD patients. Baseline urine levels of cf-mtDNA and cf-nDNA could predict renal outcomes at 6 months. Conclusions Urinary cf-mtDNA and cf-nDNA may provide novel prognostic biomarkers for renal outcome in CKD patients. The levels of plasma cf-nDNA and plasma NGAL are significantly correlated with the severity of CKD.

Additional file 3. Figure S3. Scatter-plots for correlation analysis between urinary cf-mtDNA and different variables. Figure S3A Correlation between urine cf-mtDNA and urine albumin/creatinine ratio. Figure S3B Correlation between urine cf-mtDNA and urine protein/creatinine ratio.

We present a multi-instrument experiment to study the effects of tropospheric thunderstorms on the mesopause region and the lower ionosphere. The sodium (Na) lidar observation and the ionospheric observation by two digital ionospheric sounders are used to study the variation of the neutral metal atoms and metallic ions above thunderstorms. The enhanced ionospheric sporadic E layer with a downward tidal phase is observed followed by a subsequent intensification of neutral Na density with an increase of 600 cm−3 in the mesosphere. In addition, the Na neutral chemistry and ion-molecule chemistry reactions are considered in the Na chemistry model to simulate the dynamical and chemical coupling processes in the mesosphere and ionosphere above thunderstorms. The enhanced Na layer in the simulation using the ionospheric observation as input is in agreement with the Na lidar observation. We find that the intensification of metallic layered phenomena above thunderstorms is associated with the atmospheric tides, as a result of the troposphere-mesosphere-ionosphere coupling.

We report simultaneous observations of sprite and gravity wave generated by a storm over Bangladesh. The origin of a concentric gravity wave can be traced to the storm region on Apr 27, 2014 over Bangladesh with a low cloud top surface temperature (175 K). After data analysis, the time period of the concentric gravity wave is found to be 8.8-8.9 minutes. The horizontal wavelength is found to be ~50 km for red emissions (~55 km for green emissions) and the horizontal phase velocity is 94.4 ± 31.7 m s-1 for red emissions (102.6 ± 29.4 m s-1 for green emissions). Using the dispersion relation of gravity wave, the elevation angle of wave propagation direction is found to be ~ 53.3 °. The sprite associated with the gravity wave was also recorded at 1534 UT on Apr 27, 2014. The initiation time of storm-generated gravity wave is estimated to be 1454 UT at which lightning activity was relatively low using lightning data. At time 1534 UT of the recorded sprite, the lightning rate was close to its maximum value. The storm-generated gravity wave could be thought as a precursor phenomenon for lightning and sprites since one of the necessary conditions for gravity wave, lightning and sprites is strong convection inside storms.

The special issue highlights the state of research efforts on the atmospheric electricity in Asia, particularly in Taiwan, China and Japan. In some ways, this can also be viewed as a commemorative issue for the ISUAL/FORMOSAT2 experiment, which officially ended its mission in July 2016. The first breakthrough on atmospheric electricity research in Taiwan was achieved through ground campaigns, including the investigations of transient luminous events (TLEs) near the vicinity of Taiwan (Su et al. 2002; Hsu et al. 2003) and gigantic jet (Su et al. 2003). From 2004 - 2016, the satellite mission of ISUAL (Imager of Sprite/Upper Atmospheric Lightning) onboard the FORMOSAT2 satellite was conducted, and a few important results are reported in (Hsu et al. 2017; this issue). The ISUAL mission is a successful international cooperation between Taiwan, USA and Japan (Chern et al. 2003; Su et al. 2005; Chen et al. 2008). The past and current TLE scientific missions include the Mediterranean Israeli Dust Experiment (MEIDEX) sprite campaign onboard the space shuttle Columbia in 2003 (Yair et al. 2003), a Japanese micro satellite SPRITE-SAT (2010-) (Takahashi et al. 2010), the Japan mission Global Lightning and Sprite Measurements on Japanese Experiment Module (JEM-GLIMS) on the International Space Station (ISS) from 2011 (Sato et al. 2015, 2017), NASA Crew Earth Observation program (2011 - 2012) (Jehl et al. 2013), and the Iriss mission by Denmarkâs first astronaut, Andreas Mogensen on the ISS (Chanrion et al. 2017). The upcoming orbit missions including ASIM (Atmosphere-Space Interaction Monitor) (Neubert 2009) and TARANIS (Tool for the Analysis of RAdiations from lightNIngs and Sprites) (Farges et al. 2017). The ISUAL mission besides being a pioneer atmospheric electricity program, also is a historic space platform dedicating to the study of TLEs in the middle atmosphere (Hsu et al. 2017; this issue).

AIM Recombinant tissue plasminogen activator (rt-PA) administration is the most prevalent treatment for acute ischemic within golden time. However, the effects of rt-PA on the kidney function in such patients remain unknown. This study determined long-term renal outcomes in patients with acute ischemic stroke receiving systemic rt-PA. METHODS We enroled patients who were hospitalized for acute ischemic stroke from January 2001 to January 2017. We applied 1:2 propensity score matching to eliminate various confounding variables. We defined surrogate renal outcomes as declining of estimated glomerular filtration rate (eGFR) greater than 30% and 50%, and chronic kidney disease (CKD) with eGFR less than 60 mL/min. We then compared the 1-year eGFR with paired t-test in patients treated with or without rt-PA. RESULTS Overall, 343 of 1739 patients received rt-PA within golden time. After 1:2 propensity score matching, their baseline characteristics were grouped as treated with rt-PA (n = 235) or not (n = 394). rt-PA-treated patients exhibited slower renal progression, including the risk of eGFR declining greater than 30% (hazard ratio (HR), 0.72; P = 0.03), risk of declining eGFR greater than 50% (HR, 0.63; P = 0.046) and risk of CKD (HR, 0.61; P = 0.005). After 1-year cohort, the rt-PA group exhibited an improved renal outcome by the paired t-test (propensity match: ΔGFR = 9.1 (95% confidence interval: 6.3, 11.8), P

Background Numerous studies have shown that exposure to air pollution, especially particulate matter (PM) with a diameter Methods In total, 317 CKD Stage 5-ND (estimated glomerular filtration rate 6.79 ± 4.56 mL/min) patients residing in central Taiwan who developed acute lung edema and initiated long-term dialysis were included in this case-crossover study. Pearson’s correlation test was used to examine the relationship of acute lung edema cases with PM2.5 levels and ambient temperature separately. Results The average PM2.5 level within the 7-day period correlated with acute lung edema incidence in the fall [adjusted odds ratio (OR) 3.23, P = 0.047] and winter (adjusted OR 1.99, P Conclusions A high PM2.5 level was associated with an increased risk of acute lung edema. High ambient temperature in hot seasons and low ambient temperature in cold seasons were also associated with increased risk. It is essential to educate these patients to avoid areas with severe air pollution and extreme ambient temperature.

The Imager of Sprites and Upper Atmospheric Lightning (ISUAL) on the FORMOSAT-2 satellite was launched in 2004 and records transient luminous events (TLEs). ISUAL is an instrument composed of an imager and a multichannel spectrophotometer which is able to measure the brightness from far ultraviolet to near infrared for TLEs and lightning flashes. Several types of TLEs have been identified, classified, and documented between 2004 and 2014. However, no statistical analyses on lightning have already been realized. In this paper, we focus on lightning flashes which did not induce TLEs. Statistics about brightness or temporal dynamic are presented from fitted waveforms from far ultraviolet to near infrared, after having corrected for atmospheric effects for each spectrophotometer channels. We demonstrate that the lightning/satellite distance and the altitude of the lightning need to be taken into account. The lightning waveforms from each spectrophotometer channel could be modeled as an exponential pulsed function which the shape could be explained by the photon propagation in the cloud. The median values at 777.4 nm are 1.63 × 10−6 W m−2 for the maximum brightness, 5.85 × 104 J for the total energy at the source, 414 µs for the full width half maximum, 620 µs for the full width at quarter of maximum, and 170 µs for the risetime. Results are compared with previous experiments performed from visible to near-infrared domains. The median temporal variables for near-infrared waveforms are shorter than the values of the UV waveforms.

The Imager of Sprites and Upper Atmospheric Lightning (ISUAL) on the FORMOSAT-2 satellite, launched in 2004, records Transient Luminous Events (TLEs). ISUAL has an imager and a spectrophotometer that observe TLEs all over the globe. Among these phenomena, elves are particularly difficult to detect. ISUAL often records events that correspond to significant far ultraviolet (FUV) emissions in the spectrophotometer but have no discernible TLEs in the imager. These FUV events are called “dim” elves. Therefore, it is important to develop mathematical tools to analyze the data to obtain a better evaluation of the number of elves and their occurrence. Multivariate approaches are applied to characterize the unlabeled events. The first approach is the principal component analysis which distinguishes two different groups, one including elves and dim elves. The second approach is the PARallel FACtor analysis which provides a waveform model for each group. These methodologies confirm that FUV signal is the evidence of TLE presence. A crude classification method was then suggested taking into account these results. The proportion of elves, relatively to the considered ISUAL data set, is found to be about 40%. It is similar to previous results and confirms that relatively weak lightning peak current is sufficient to produce elves. This new strategy demonstrates the potential for discriminating between lightning and TLEs without prior knowledge within the selectivity of the FUV spectral band.

Thunderstorms are electric generators, which drive currents upwardly into the ionosphere. In this paper, we examine the effects of thunderstorm upward current on the ionosphere. We use a thunderstorm model to calculate the three-dimensional current flows in the atmosphere and to simulate the upward current above the thunderstorm with the tripole-charge structure. The upward current flows into the ionosphere, while the associated electric field causes the plasma E × B motion. The caused plasma motion redistributes the plasma density, leading to ionospheric density variations. In the nighttime ionosphere, the E × B motion may also cause the formation of plasma bubbles.

The Imager of Sprites and Upper Atmospheric Lightning (ISUAL) has been operated for more than ten years. The onboard spectrophotometer channel-1 (SP1) was designed to detect the far-ultraviolet (FUV) emissions (N2 Lyman-Birge-Hopfield band) from space. It was found that most of the transient luminous events (TLEs), such as sprites, halos, elves, and gigantic jets, are usually accompanied by FUV emissions. The FUV emission could be utilized as an indicator for searching TLEs because the FUV emission of lightning is severely attenuated in the atmosphere during propagation, although the TLE FUV emissions are still detectable. Furthermore, the elves FUV emission photon flux can also be used to estimate the parent lightning peak current. Therefore, SP1 sensitivity degradation assessment, which affects the observed intensity of FUV emissions, is important. Although ISUAL has a light-emitting diode (LED) which is preset as a standard light source, the emission wavelength range of the LED does not cover the FUV band. We established a method in this study to determine the ISUAL Imager and SP1 sensitivity degradation. We found that the annual degradation rates of the ISUAL Imager and the SP1 are 8.4 and 9.7%, respectively.

Observing from southern Taiwan on 2 August 2010, a thunderstorm near Luzon Island, Philippines, about 500 km away was found to produce 72 transient luminous events (TLEs). Besides optical images, ULF and VLF sferics of lightning from this thunderstorm were also recorded. This work examines the characteristics of TLE-producing lightning through studying their ULF and VLF sferics. The attenuation of ULF and VLF sferics in the Earth cavity is obtained through analyzing the sferics associated with Imager of Sprite and Upper Atmospheric Lightning elves that occurred within ~1500 km of Taiwan. Amplitudes of the ULF and the VLF sferics are found to vary as D−0.871 and D−1.207, respectively, where D is the source distance from the sferic stations. After normalizing the sferics from the 2 August 2010 storm to 500 km distance, the ratio of the peak ULF and the VLF magnetic fields is found to be distinct for different TLE-producing lightning. The ratio for the halo-producing lightning is nearly 3 times that of the elve-producing lightning, but it is comparable to that of the halo-sprite-producing lightning, although the ULF strength for the halo-sprite lightning is significantly larger than that for the halo lightning. Therefore, it is possible to distinguish between the TLE-types using the ULF to VLF peak ratio or the strength of ULF/VLF band emissions of the parent lightning. Comparison of numerically simulated and the observed lightning radiation fields indicates that the best fit discharge time of the elve lightning is about 100 µs, while that for the halo-producing lightning is between 200 and 500 µs.

In our previous model for the lithosphere-atmosphere-ionosphere coupling, the background magnetic field was assumed to be perpendicular to the horizontal plane. In the present paper, we improve the calculation of currents in the atmosphere by solving the current density J directly from the current continuity equation ∇ • J = 0. The currents in the atmosphere can be solved for any arbitrary angle of magnetic field, i.e., any magnetic latitude. In addition, a large ratio (~10) of Hall to Pedersen conductivities is used to generate a large Hall electric field. The effects of atmospheric currents and electric fields on the ionosphere with lithosphere current source located at magnetic latitudes of 7.5°, 15°, 22.5°, and 30° are obtained. For upward (downward) atmospheric currents flowing into the ionosphere, the simulation results show that the westward (eastward) electric fields dominate. At magnetic latitude of 7.5° or 15°, the upward (downward) current causes the increase (decrease) of total electron content (TEC) near the source region, while the upward (downward) current causes the decrease (increase) of TEC at magnetic latitude of 22.5°or 30°. The dynamo current density required to generate the same amount of TEC variation in the improved model is found to be smaller by a factor of 30 as compared to that obtained in our earlier paper. We also calculate the ionosphere dynamics with imposed zonal westward and eastward electric field based on SAMI3 code. It is found that the eastward (westward) electric field may trigger one (two) plasma bubble(s) in the nighttime ionosphere.

[1] We report the ionization emission associated with N2+ 1N band in a halo event without visible sprite streamers. To avoid the lightning contamination to the ionization emission, we find halos whose parent lightning light is blocked by the Earth's limb. Five halos in the 2004–2010 Imager of Sprites and Upper Atmospheric Lightning data set were identified as halos without visible sprite streamers. A halo with maximum N2 1P brightness had significant ionization emission of N2+ 1N. The time-integrated photon intensity of N2 1P, N2 2P, and N2+ 1N emission is 2.2 × 105, 2.1 × 104, and 7.4 × 102 photons cm−2, respectively at a distance of 4130 km. The total number of photons of N2 1P, N2 2P, and N2+ 1N band emissions are 4.6 × 1023, 4.3 × 1022, and 1.6 × 1021 photons, respectively. In the halo region, the electron density increased as 1–2 orders of magnitude higher than ambient electron density. From the emission ratio of N2+ 1N to N2 2P, the reduced electric field is estimated to be 275–325 Td that is higher than the conventional breakdown electric field. The recorded electric field related to this halo event is produced by a lightning discharge that has a total charge moment change of −1450 C km. Based on the estimated electric field from optical emissions, it is found that the lightning-induced electric field in the bright halo region is significantly relaxed with a rate faster than that estimated using ambient electron density, in agreement with previous modeling results showing that the electron density enhancement due to the ionization processes leads to a short dielectric relaxation time inside the halo region.

[1] Three multi-transient luminous events, which were recorded by ISUAL on FORMOSAT-2 and shared a similar generating sequence, are reported. Each event began with a positive cloud-to-ground lightning discharge (CG)-induced sprite, and a secondary gigantic jet (GJ) followed within ~30–50 ms. Then, 1 ms after the GJ, a new sprite occurred near the GJ without associated impulsive lightning signal. The associated electromagnetic signal for one of the events indicates that the GJ is a negative cloud-to-ionosphere discharge carrying a high peak current moment. Cross-analysis of the spectral, image, and electromagnetic data of these three events indicates that the new sprites are likely induced by the secondary GJs, and the high current moment of the secondary GJs appears to be a crucial factor for the induction of the new sprites. Hence, these secondary GJs may have played a role in inducing sprites as much as the negative CGs do for the occurrence of negative sprites.

In Taiwan, research and education of solar terrestrial sciences began with a ground-based ionosonde operated by Ministry of Communications in 1952 and courses of ionospheric physics and space physics offered by National Central University (NCU) in 1959, respectively. Since 1990, to enhance both research and education, the Institute of Space Science at NCU has been setting up and operating ground-based observations of micropulsations, very high-frequency radar, low-latitude ionospheric tomography network, high-frequency Doppler sounder, digital ionosondes, and total electron content (TEC) derived from ground-based GPS receivers to study the morphology of the ionosphere for diurnal, seasonal, geophysical, and solar activity variations, as well as the ionosphere response to solar flares, solar wind, solar eclipses, magnetic storms, earthquakes, tsunami, and so on. Meanwhile, to have better understanding on physics and mechanisms, model simulations for the heliosphere, solar wind, magnetosphere, and ionosphere are also introduced and developed. After the 21 September 1999 Mw7.6 Chi–Chi earthquake, seismo-ionospheric precursors and seismo-traveling ionospheric disturbances induced by earthquakes become the most interesting and challenging research topics of the world. The development of solar terrestrial sciences grows even much faster after National Space Origination has been launching a series of FORMOSAT satellites since 1999. ROCSAT-1 (now renamed FORMOSAT-1) measures the ion composition, density, temperature, and drift velocity at the 600-km altitude in the low-latitude ionosphere; FORMOSAT-2 is to investigate lightning-induced transient luminous events, polar aurora, and upper atmospheric airglow, and FORMOSAT-3 probes ionospheric electron density profiles of the globe. In the near future, FORMOSAT-5 and FORMOSAT-7/COSMIC-2 will be employed for studying solar terrestrial sciences. These satellite missions play an important role on the recent development of solar terrestrial sciences in Taiwan.

This paper presents a literature survey on the recent developments related to experimental and modeling studies of transient luminous events (TLEs) in the middle atmosphere termed elves, sprites and jets that are produced in association with thunderstorm activity at tropospheric altitudes. The primary emphasis is placed on publications that appeared in refereed literature starting from year 2008 and up to the present date. The survey covers general phenomenology of TLEs and their relationships to characteristics of individual thunderstorms and lightning, physical mechanisms and modeling of TLEs, past, present and future orbital observations of TLEs, and their chemical, energetic and electric effects on local and global scales.

Sprites, elves and blue jets are collectively denominated as the upper atmospheric transient luminous events (TLEs). They are recently discovered optical flashes between active thunderstorms and the ionosphere. In this report, a brief introduction to the most important characteristics of TLEs is given. Since 2001, scientists from the National Cheng Kung University have been performing yearly summer campaigns from various locations in Taiwan. The main achievements of their yearly campaign are presented.

Transient luminous events (TLEs; sprites, elves, jets and etc.) are lightning-related optical flashes occurring above thunderstorms. Since the first discovery of sprites in 1989, scientists have learned a great deal about the morphological, spectroscopic and electromagnetic characteristics of TLEs through ground and spacecraft campaigns. However, most of the TLE studies were based on events recorded over US High Plains. To elucidate the possible biasing effects, space-borne observations are needed and have their merits. Imager of sprites and Upper Atmospheric Lightning (ISUAL) on the FORMOSAT-2 satellite is the first instrument to carry out a true global measurement of TLEs from a low- earth orbit. In this short paper, we apply a common astronomical data analysis technique, two-color diagram, on the ISUAL spectrophotometer (SP) data. By choosing appropriated bandpasses and converting the measured flux of TLEs into the unit of magnitude, two-color diagrams of TLEs can be constructed. We demonstrate that two-color diagrams, which were constructed from the narrow-band spectrophotometer data, can be used to classify different types of TLEs and trace their temporal evolution. The amount of reddening due to Earth`s atmosphere can also be estimated from two-color diagrams assembled from the broad-band spectrophotometer data.

[1] On 31 August 2010, more than 100 transient luminous events were observed to occur over Typhoon Lionrock when it passed at ∼210 km to the southwest of the NCKU site in Taiwan. Among them, 14 negative gigantic jets (GJs) with clear recognizable morphologies and radio frequency signals are analyzed. These GJs are all found to have negative discharge polarity and thus are type I GJs. Morphologically, they are grouped into three forms: tree-like, carrot-like, and a new intermediate type called tree-carrot-like GJs. The ULF and ELF/VLF band signals of these events contain clear signatures associated with GJ development stages, including the initiating lightning, the leading jet, the fully developed jet, and the trailing jet. Though the radio waveform for each group of GJs always contains a fast descending pulse linked with the surge current upon the GJ-ionosphere contact, the detailed waveforms actually vary substantially. Cross analysis of the optical and radio frequency signals for these GJs indicates that a large surge current moment (CM) (>60 kA-km) appears to be essentially associated with the tree-like GJs. In contrast, the carrot-like and the tree-carrot-like GJs are both related to a surge CM less than 36 kA-km, and a continuing CM less than 27 kA-km further separates the carrot-like GJs from the tree-carrot-like GJs. Furthermore, on the peak CM versus charge moment change diagram for the initiating lightning, different groups of GJs seem to exhibit different trends. This feature suggests that the eventual forms of negative GJs may have been determined at the initiating lightning stage.

[1] A full kinetic elve model with a wide time range from microseconds to seconds and its spectral range from UV, visible to near-infrared wavelengths is developed. Not only the fast electron-impact emissions N2 1P (B3Πg- A3Σu+), N2 2P(C3Πu- B3Πg), N2Lyman-Birge-Hopfield (a1Πg- X1Σg+), N2+ 1N (B2Σu+- X2Σg+) and O2+ 1N (b4Σg− – a4Πu) but also the post-impulse chemiluminescenses, O2 atmospheric band (b1Σg+ – X3Σg−), O(1S – 1D) at 557.7 nm and O(1D – 3P) at 630 nm, are considered in the elve model. We calculate the dominant emissions and possible weak emissions in our elves model to analyze the relative importance of emission intensity, measured by the ISUAL imager with 5 selectable band pass filters (N21P, 762, 630, 557.7, 427.8 nm filter). The modeling emission intensities were well consistent with the measurements by Imager with different filters. This comparison could also be useful in designing the imager filters for future TLE survey missions in Earth orbit.

[1] Secondary transient luminous events (TLEs) recorded by the ISUAL-FORMOSAT2 mission can either be secondary jets or secondary gigantic jets (GJs), depending on their terminal altitudes. The secondary jets emerge from the cloud top beneath the preceding sprites and extend upward to the base of the sprites at ∼50 km. The secondary jets likely are negative electric discharges with vertically straight luminous columns, morphologically resembling the trailing jet of the type-I GJs. The number of luminous columns in a secondary jet seems to be affected by the size of the effective capacitor plate formed near the base of the preceding sprites and the charge distribution left behind by the sprite-inducing positive cloud-to-ground discharges. The secondary GJs originate from the cloud top under the shielding area of the preceding sprites, and develop upward to reach the lower ionosphere at ∼90 km. The observed morphology of the secondary GJs can either be the curvy shifted secondary GJs extending outside the region occupied by the preceding sprites or the straight pop-through secondary GJs developing through the center of the preceding circular sprites. A key factor in determining the terminal height of the secondary TLEs appears to be the local ionosphere boundary height that established by the preceding sprites. The abundance and the distribution of the negative charge in the thundercloud following the sprite-inducing positive cloud-to-ground discharges may play important role in the generation of the secondary TLEs.

[1] This study revisits the sprite polarity paradox, first manifest by observations that exceptional cloud-to-ground flashes with negative polarity generally did not produce detectable sprites. The paradox is here resolved by the Transient Luminous Event (TLE) known as the halo, which on account of its inferior brightness (0.3 MR versus 1.5 MR) and substantially shorter duration (1 ms versus 10–100 ms) in comparison with the sprite, is not readily detectable in ground-based video cameras with standard field duration (16.7–20 ms). Observations with improved temporal resolution (ISUAL (Imager of Sprites and Upper Atmospheric Lightnings) from space and PIPER (Photometric Imager of Precipitated Electron Radiation) observations from the ground) provide evidence that flashes with negative polarity dominate the global halo population, and that the halo numbers are more than sufficient to account for the previously missing TLEs. The evidence for lightning polarity-dependent TLEs (sprites, positive and halos, negative) is attributable to the well established but incompletely understood contrast in the behavior of negative and positive lightning flashes to ground.

[1] We analyzed the ISUAL-FORMOSAT2 elves, the LIS-TRMM lightning, the sea surface temperature (SST), and the El Nino southern oscillation (ENSO) indices (the Nino 3.4 Index and the Southern Oscillation Index - SOI) in the period between June 2005 and May 2010 to explore the impacts of ENSO on the occurrences of the mesospheric elves and the troposphere lightning. The standardized anomalies of the elve and the lightning occurrence densities are used to quantify the deviation of the elve and lightning occurrences during an ENSO event. The areas in the ENSO-sensitive western Pacific, central Pacific and Tahiti regions with a significant event anomaly are taken to be the impact indicators of ENSO. Also the SOI is used to examine the correlation of the temporal intensity variation between ENSO, elve and lightning. The results indicate that elve shows clear responses to ENSO with a correlation over 0.6 in the coastal and the oceanic regions. The lightning occurrence is responsive to ENSO in the oceanic regions, but shows a low correlation in the coastal regions, due the overwhelming influence of the landmass. Therefore, between elve and lightning as proximity indices of ENSO, elve has a broader applicable geographic range. However, elve is known to be the mesospheric luminous manifestations of the high-peak-current lightning, and the response of the intense lightning to ENSO would be similar to that of the elve. Hence, alternatively, the intense lightning can also be used as an indicator of ENSO.

In the past 6 years, the ISUAL payload onboard the Taiwanese FORMOSAT-2 satellite has successfully carried out the primary mission of performing a global survey of transient luminous events (TLE) and lightning activities. The observation data have been used to construct the first global distribution map of TLEs and to infer their occurrence rates. To register dim TLE emissions at night, ISUAL employs electron-multiplying devices like a photomultiplier, multi-anode array, and micro-channel plate to intensify the photons emitted by transient events. These devices, however, will degrade gradually with age. The degradation rate and the performance change were monitored through periodic calibration observations and are investigated carefully in order to achieve precise photometry and accurate statistics. The annual degradation rates up to 14% were identified for some of the sensor elements. This paper presents the variations of instrument efficiencies and overall detection capabilities, before and after applying a gain-adjustment to compensate for sensor degradation. The resulting stable trend of the ISUAL trigger and lightning rates suggests that the bias from instrument degradation and gain adjustments is minimal. This point is also supported by the near constant sprite and halo detection rates deduced from different statistical temporal intervals. Hence, the anomalies in the ISUAL elve detection rate for 2008 ~ 2009 likely are due to the El Niño and Southern Oscillation (ENSO) events. Forecast based on the ISUAL performance trend also indicates that the ISUAL sensors have sufficient sensitivity margins to operate efficiently until the end of 2013, or even beyond.

The Imager of Sprites and Upper Atmospheric Lightning (ISUAL) experiment on the FORMOSAT-2 satellite inferred the global occurrence rates of sprites, halos and elves to be ∼1, ∼1 and 35 events/min, respectively [1, 2]. Hence, elve is the most abundant type of transient luminous events (TLEs). From analyzing brightness observed by ISUAL Imager through different filters (1PN 2 , 762, 630, 557.7, 427.8 nm), the relative intensity of the OH (9,3), O1D, O1S, 1NN 2 + and O 2 Atmosphere band (0,0) emissions in elves will be discussed.

[1] On 22 July 2007, 37 blue jets/starters and 1 gigantic jet occurring over a thunderstorm in the Fujian province of China were observed from the Lulin observatory on the central mountain ridge of Taiwan. The majority of the jets were observed to occur in a 5 min window during the mature phase of the jet-producing thunderstorm. These jets have significant red band emissions. However, the blue emissions from these jets were not discernible due to severe atmospheric scattering. A model estimation of the emissions from a streamer reveals that the red emissions in blue starters and blue jets are mainly from the nitrogen first positive band (1PN2). The type II gigantic jet is the first of this type that was observed from the ground. The generation sequence of the gigantic jet begins with a blue starter, then a blue jet occurs at the same cloud top after ∼100 ms and finally develops into a gigantic jet ∼50 ms later. Using “optical strokes” as surrogates of the lightning strokes, the correlations between jets and the cloud lightning are explored. The results indicate that the occurrence of jets can be affected by the preceding local cloud-to-ground (CG) lightning or nearby lightning (intracloud (IC) or CG), while in turn the jets might also affect the ensuing lightning activity.